A179996 - OEIS

A179996

Composite numbers n such that Sum_{k=0..q} d(k)*10^k is prime where d(k) are the q+1 distinct prime factors of n, d(0)< d(1) < ... < d(q).

15, 21, 33, 45, 51, 57, 63, 69, 75, 87, 91, 93, 99, 111, 129, 133, 135, 147, 153, 165, 171, 177, 183, 187, 189, 201, 207, 217, 219, 225, 253, 255, 261, 273, 279, 297, 303, 309, 327, 333, 363, 375, 387, 399, 405, 411, 427

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OFFSET

1,1

LINKS

Table of n, a(n) for n=1..47.

EXAMPLE

435 is in the sequence because the prime divisors of 435 are {3, 5, 29} and

3 + 5*10 + 29*100 = 2953 is prime.

MAPLE

with(numtheory):T:=array(1..10) : for n from 1 to 1000 do:x:=factorset(n):

k:=nops(x):s:=0:for i from 1 to k do:s:=s+x[i]*10^(i-1) :od:if type(s, prime)=true

and k > 1 then printf(`%d, `, n):else fi:od:

MATHEMATICA

cnpQ[n_]:=Module[{pd=FactorInteger[n][[All, 1]]}, Length[pd]>1&&PrimeQ[ Total[ pd*10^Range[0, Length[pd]-1]]]]; Select[Range[500], cnpQ] (* Harvey P. Dale, Sep 02 2022 *)

CROSSREFS

Sequence in context: A177516 A127329 A043326 * A079814 A168354 A190358

Adjacent sequences: A179993 A179994 A179995 * A179997 A179998 A179999

KEYWORD

nonn,base

AUTHOR

Michel Lagneau, Jan 13 2011

STATUS

approved